Case Study 1: A 10-year old girl is brought in to Green Meadows Clinic because of redness, pain, and swelling of the left hand. According to her mother, the day before the onset of her symptoms, the child was accidentally bitten by her cat. Physical exam reveals temperature of 37.8 degrees C, enlarged axillary lymph nodes and erythematous and swollen left had that was hot to touch. The pain now has spread upward and involved the upper arm. An atending physician notics early sins of abcess formation and accumulation of pus at the bite site. A presumptive diagnosis is made and the purulent exudate sent for culture.

What is the most likely diagnosis?

What is the most likely cause?

Cat-bite cellulitis

Pasteurella multocida

Case 2: A 2-month-old male infant was brought to the peditrician because of coughing and chocking spells for two weeks. At the end on the coughing spell, teh baby often vomited and sometimes seemed to have difficulty catching his breath. The nurse in the clinic noted that the cough was paroxysmal. The mother related that she had had coughing spells followed by choking and near vomiting for three weeks. She had recieved a course of amoxicillin withour relief. ON evaluation, the baby's temperature was 37.7 degrees C (↑); pulse, 200/min (↑); respiration 72/min (↑); WBC, 140,000/mm3 (↑↑↑) of which 50% were lymphocytes (↑↑). Chest x-ray revealed upper lobe infiltrates bilaterally and patchy infiltrates in teh middle lobes consistent with pneumonia. The infant was admitted to pediactric ICU where he was intubated and placed on a mechanical ventilator.

in order to differentiate between the different streps, it is important to look at hemolysis

beta-hemolytic is the MOST pathogenic

alpha-hemolysis does not always meano pneumo, it can also be various other viridans (also strepto but don't have to remember the names!)

beta = GAS, GBS

alpha = S. pneumo, viridans

non-hemolytic = E. fae, S. bovis (GDS)

viridans

streptococci

viri-green

normal flora in throat (nasopharyngeal)

if it moves through the blood dtream and lodge in heart, can cause sub-acute endocarditis

important clinical relevance: "clenced-fist syndrome"--hit someone in the mouth, fingers have little padding, therefore bane makes contact with teeth. If teeth have viridans bacteria and they get into bone, osteomyeletis can occure

why it is important to perform Optochin test and differentiate between S. pneumo and alpha-hemolytic viridans streptococci

Staphylococcus aureus

G+ cocci

on a BAP media--colony morphology: NARROW zone of beta-hemolysis around colonies; LARGE GOLDEN colonies; creamy appearance on plate

TEST OF CHOICE = Optpchin Test: Optochin is a detergent that causes the autolysins in S. pneumo to work to dissolve itself; ZOne of growth inhibition around the optpchin disc in the BAP media; Bile is another alternative to optochin disk; thisis how we differentiate s. pneumo from other viridans

Enterococcus faecalis (E. fae) aka Streptococcus faecalis

G+ cocci

on a BAP media--colony morphology: NO hemolysis; MEDIUM GRAY-sh colonies

microscopic morphology: strep = chains

nosocomial--hospital acquired infections

E. fae and S. bovis (GDS) are similar in appearance on plate

clinical relevance of distinguishing of differentiating between the 2: S. bovis is linked to colon cancer; of you get colon cancer you will inevitably get S. bovis; if you have S. bovis they should check you for colon cancer

TEST OF CHOICE = Bile Esculin Agar: Both E. fae and S. bovis will hydrolyze esculin to esculetin therefore turning the plate black--then do: 6.5% NaCl growth test: differentiates the two bacteria; E, fae will grow (+) (because it is used to being in low pH of the GI tract) where as S. bovis will not (-)

differentail (mannitol) mannitol can fermented by S. aureus, so this media differentiates S. aureus from other staph (becuase it is the only on that can ferment mannitol)

mannitol fermentation results in acid production, pink → yellow

when you streak for isolation in this media, a section of it will remain pink, why? becuase the isolated colonies don't have enough bacteria to produce enough acid to perform a color change like on the rest of the plate, or colonies simply did not grow there at all

test break down

S. sureus = mannitol and coag/cat test

GAS = BAC

GBS = CAMP

S. pneumo = optochin

H. flu = satalite

Medically Important Enterobacteriaceae (Lab)

All members are G- rods, ferment glucose, reduce NO3 to NO2

Clinical Relevance: The most common cause of UTI in females is E. coli. Numerous other bacteria can cause UTI's though, so in order to differentiate what bacteria it is, doctors will measure the NO2 in the urine. Because it is formed by E. coli, the patient's will have high level in their urine if they have a UTI caused by E. coli.

Look essentially the same on blood agar

On MacConkey agar: Lac+(pink) and Lac-(colorless)

Produce distinctive patterns on TSI, Indole, and Urea tests (T-I-U)

First, look at colony Morphology and patterns of Lactose use on MacConkey agar

E. coli (lac+/-)

Klebsiella pneumoniae (lac+)

E. coli 0157:H7 (lac+)

Shigella sp. (lac-)

Proteus sp. (lac-)

However, colony morphology alone is not enough to ID the organisms

T-I-U

3 tests: Triple Sugar Iron (TSI); Indole (Tryptone); Urease (Urea)

It is necessary to observe the patterns of all three tests (T-I-U) in order to make an accurate diagnosis.

Intact T-I-U

Each organism has its own distinct pattern on T-I-U tests

Allows presumptive ID on most Enterobacteriaceae members

Test #1 Triple Sugar Iron (TSI) contains:

The contents of the tube are red before adding that bacteria because it is made up of peptone (peptides) which is a Nitrogen source

Triple sugars: glucose, sucrose, lactose

Nitrogen source peptone (peptides)

Sulfur source: sodium thiosulfate which can then be converted to H2S and bind to iron (if H2S is produced, remember the butt turns black)

Iron: H2S indicator

pH indicator: phenol red, turns yellow in acidic conditions (when the bacteria ferments the sugar)--Remember: if it turns yellow, it is fermenting that sugar, therefore it is positive for that sugar

TSI section A

The slant = TOP

Indicates if the bacterium can ferment lactose in addition to glucose

If the organism can't lactose, it uses peptides after using up glucose → NH3+ → makes slant alkaline (pink)

The production of bubbles is due to CO2: This may be hard to see on a test. This is important when dealing with Klebsiella, which has lots of gas produced.

Indicates the ability of the bacteria to produce the enzyme urease, which converts urea → NH3 (ammonia) + CO2

Color change due to pH change (alkaline)

Yellow (acidic) to Rose (alkaline) or Magenta (alkaline)

Strength of pink color is dependent upon how much ammonia is produced

E. coli can be Lac+ or Lac-

This makes a big differences on the Mac plate and in the TSI patteren you see

Most E. coli are Lac+

The one that is Lac- is EIEC

4 different types to know: EIEC, EHEC, ETEC, EPEC

ALL are indole +

ALL are urease -

EIEC: ONLY one the is lac-, TSI: red/yellow (lac-/glu+)

EHEC (aka E. coli 0157:H7): ONLY one that is sorbitol- (grows colorless on a sorbitol half plate), clinical relevance: HUS-shigatoxin damages the inside of blood vessels (capillaries) of the glomerulus in the kidney, therefor sends patient into KIDNEY FAILURE

EHEC, ETEC, EPEC: TSI: yellow/yellow (lac+/gluc+)

E. coli0157:H7

Another exception

Test: Streak on a Sorbitol-MacConkey biplate

This is the only E. coli that is colorless on sorbitol

Regular E. coli will appear pink on both sides of the Sorbitol-MacConkey biplate, while 0157:H7 will be pink ONLY on the MacConkey agar side

E. coli 0157:H7 = EHEC

T-I-U for Lac+ E. coli

TSI: Yellow/Yellow

Indole: always positive

Urease: negative

For Lac-, the ONLY diffference is TSI: Red/Yellow

T-I-U for Klebsiella pneumoniae

TSI: Yellow/Yellow (lac+/glu+) often with lots of gas

Indole: Negative

Urease: Weak Positive that results in rose color

MacConkey: PINK because lac+

T-I-U for Shigella

TSI: Red/Yellow (lac-/glu+)

Indole: Negative

Urease: Negative

MC: COLORLESS bacuse lac-

Proteus spp.

Proteus will not form any single colonies on a BAP

Instread colonies produce "SWARMING" (key word)

Swarming happens only on BAP and ONLY with Proteus spp.

T-I-U for Proteus spp.

TSI: Red/Black (lac-/glu+/H2S+)

Indole: depends on species--p. vulgaris (+); p. mirabilis (-)

Urease: Strong Positive that results in magenta color

MC: COLORLESS because lac-

PUTRID, terrible, NASTY smell

T-I-U for Salmonella:

TSI: Red/Black (Slight yellow in the bottom of butt) (lac-/glu+/H2S+)

Indole: Negative

Urease: Negative

MC: COLORLESS because lac-

Klebsiella and Proteus are both urease positive:

Can differentate on color intensity:

Proteus = Magenta

Klebsiella = Rose

which 2 pathogens are urease +

Kllebisella (rose)

Proteus--both kinds (magenta/hot pink)

which two pathogens are indole +

E. coli (all)

Proteus vulgaris

EIEC?

lac-

EHEC (O157)

sorbitol-

all E. coli?

indole+, urease-

LAC-?

SSEP (shigella, salmonella, proteus, e. coli)

LAC+?

KE (klebsilla, and e. coli)

GI Pathogens:

For the GI Pathogens:

Campylobacter jejuni

Shigella spp.

E. coli

Salmonella

You should know:

General Traits

Key virulence factors

Epidemiology

Pathogens

Treatment and Prevention

General characteristics for Campylobacter jejuni:

Motile

Comma or spiral-shaped

Gram (-)

Oxidase (+)--grows poorly in O2

Microaerophilic (grow at 5% O2, 10% CO2)

Prefers 42°C (normal avian body temp)

C. jejunji of on Skirrow medium" Selective blood agar plate supplemented with antibiotics and antimycotics to inhibit other intestinal organisms